Hide text in text field

[sisira]

I want to hide part of the text embeded to a text field.

As an examople,
by default the end part of the text field should be part of a email address (@yahoo.com). This part should not be viewed by the page visitors. But They must be given the option to fill the first part of the email.]

How can i do this
please help me

[leatherback]

well... If you a priori know what the extention is, you can just add the string server-side, couldn't you? Why have the hidden text?